Microorganism is a general term for tiny organisms which are widely distributed in nature and not visible to the naked eye, but can only be observed being magnified under an optical microscope or an electron microscope by hundreds, thousands or even tens of thousands of times. They have characteristics such as a tiny size, a simple structure, rapid reproduction, easy variation and strong adaptive capacity to environment.
The microorganisms are of wide varieties, and are extremely widely distributed in nature. Human, animals and plants carry a variety of microorganisms are also present on body surfaces and cavities communicating with the exterior.
One of the most important influences of microorganisms on human is to cause some diseases, especially infectious diseases. Although great progresses have been made in the prevention and treatment of diseases, newly occurring and recurring microbial infections continue to appear, and effective therapeutic drugs against many diseases are lacking all the time. Furthermore, the strong selection pressure caused by the overuse of a large number of broad-spectrum antibiotics lead many strains to mutate, resulting in the appearence of more dangerous drug-resistant strains.
All microorganisms growing in a living body in vitro or in vivo are called parasitic microorganisms, and the microorganisms in parasitic life-style make a living by depriving nutrition of other organisms, even depending on some parts of the bodies of other organisms as nutrients. Microorganisms can enter a human or animal body through the mouth, skin or respiratory tract, and grow and reproduce making use of the nutrition of the human or animal body. If these bacteria produce toxins, humans will be met with illnesses such as cholera, typhoid and pneumonia. Diseases such as AIDS and common cold are caused by viruses. Viruses are more specific parasitic microorganisms; because they cannot live away from living cells, they are called as strictly parasitic microorganisms.
Microbial infections are common clinical diseases caused by microorganisms. For the diagnosis of most of bacterial diseases, bacteriological diagnosis is required in order to determine the causes of diseases. However, some bacteria being isolated from a specimen does not necessarily mean that this bacterial species is the pathogen of the disease, and thus a comprehensive analysis shall be performed according to the clinical situation of the patient, the specimen collection site, and the species of the isolated bacteria. Sometimes virulence, cell and animal tests shall be made to determine pathogenicity of the strain.
Since bacteria and their metabolites have antigenicity, bacterial infections can also be diagnosed by detecting antibodies. Furthermore, gene diagnosis, a new method for diagnosing bacteria by detecting genetic materials of bacteria, is developed in recent years. However, the detection method mentioned above requires tedious operation, strict conditions in the collection and preservation of samples, and a long detection period, which could easily lead to delays of the patient's condition, but produces a high false positive rate in the test results.
Laboratory tests for virus infection include viral isolation and identification, direct detection of viral nucleic acids and antigens, and detection of specific antibodies. A defect of the existing viral detection methods is in that the requirements on the collection, storage and transportation of samples required for the virus detection are more stringent, and the sample collection is easily affected by subjective factors of the collector, resulting in high false positive or negative rate of the virus detection that can affect the clinical outcomes.
An infectious disease, especially a chronic persistent infection, is one of global stubborn diseases harmful to the human health and life. Intracellular pathogens forming a significant impact on human include Mycobacterium tuberculosis, Salmonella, Brucella, Legionella pneumophila, Listeria, and Mycobacterium leprea. Seven diseases, including tuberculosis, AIDS and hepatitis, form global threats, and are difficult to treat for the reason closely relating to the intracellular parasitism of pathogens.
It is a tough problem to treat intracellular microbial infections. The main reason includes: when the pathogens invade and lie dormant in the cells, it is difficult to deliver a conventional antibiotic to the cells where the pathogens hide, and even if delivered, it is difficult to achieve an effective microbicidal effect at the concentration of antibiotic; antibodies could hardly enter the cells to play a role; and when the intracellular bacteria are successfully living in cells, they could not only escape from the immune phagocytosis, killing and clearance, but also exist for a long time in the cells and lead to physical diseases when the time is convenient (e.g., when immunity of the body decreases).
Therefore, new diagnostic and therapeutic techniques are in urgent need for microbial infectious diseases with simple operation and accurate results so as to improve the laboratory diagnosis and clinical treatment of such diseases, and to avoid delays of the patient's condition and reduce the physical and economic burden of patient.